$ A = \left[\begin{array}{rrr}2 & 1 & 1 \\ 1 & 0 & 2 \\ 2 & 2 & 1\end{array}\right]$ What is $ A^{-1}$ ?
Solution: $ = \left[\begin{array}{rrr}\frac{4}{3} & -\frac{1}{3} & -\frac{2}{3} \\ -1 & 0 & 1 \\ -\frac{2}{3} & \frac{2}{3} & \frac{1}{3}\end{array}\right]$